1. Field of the Invention
The present invention relates to a semiconductor device and manufacturing method of the same, and more particularly to a technology that can be effectively employed in semiconductor devices used in RF (Radio Frequency) power modules and manufacturing technology of the same.
2. Description of the Related Art
In recent years, mobile communication devices (the so-called portable phones) represented by communication systems GSM (Global System for Mobile Communications), PCS (Personal Communication Systems), PDC (Personal Digital Cellular) systems, and CDMA (Code Division Multiple Access) systems became popular throughout the world.
Generally, such mobile communication devices comprise an antenna for emitting and receiving electromagnetic waves, a high-frequency power amplifier (RF power module) for amplifying the high-frequency signal that was power modulated and supplying it to the antenna, a reception unit for processing the high-frequency signal received by the antenna, a control unit for controlling the above-described units, and a battery for supplying a power source voltage thereto.
JP-A-2004-221344 describes a technology for forming a field plate electrode on the side surface of the gate electrode on the drain side thereof by using a photoresist film as a mask and dry etching a polysilicon film.
Compound semiconductor devices such as HBT, and HEMT, silicon bipolar transistors, and LDMOSFET (Laterally Diffused Metal-Oxide-Semiconductor Field Effect Transistor, laterally diffused MOSFET) have been used as amplification elements used in power amplification circuits of RF power modules of mobile communication devices according to the application object or state thereof.
Among those amplification elements, LDMOSFET employ a structure in which a high drain breakdown voltage is ensured by providing a drain region with a high dopant concentration on the drain side via an offset drain region with a low dopant concentration. The advantage of such a structure is that though the power addition efficiency is lower than that of the compound semiconductor devices, bias is easy to control and mass productivity is higher.
Diversification and globalization of cellular phones resulted in a steady improvement of performance required for RF power modules and amplification elements (semiconductor chips for amplification) used therein. For example, in performance evaluation of amplification elements (semiconductor chips for amplification) used in RF power modules, a high addition efficiency (power efficiency) is regarded as very important. Therefore, it is necessary to provide RF power modules and amplification elements (semiconductor chips for amplification) used therein that have improved performance such as addition efficiency. Forming a metal silicide film on the front surface of a gate electrode, etc., to decrease the electric resistance thereof is considered as means for increasing the addition efficiency.
With the technology of forming a field plate electrode on the side surface of the gate electrode on the drain side thereof by using a photoresist film as a mask and dry etching a polysilicon film, an alignment margin of the photomask and gate electrode is necessary with consideration for the misalignment of the photomask associated with the accuracy of the exposure apparatus or the like. For this reason the upper end portion of the field plate electrode is formed so as to cover part of the upper portion of the gate electrode. When a silicide process is applied to such a structure, the field plate electrode extends on top of the gate electrode. Therefore, the metal silicide film cannot be formed on the entire upper surface of the gate electrode.
It is an object of the present invention to provide a technology capable of improving the performance of a semiconductor device.
This and other objects as well as novel features of the present invention will become apparent from the following specification and accompanying drawings.